Increase delay when after eventually consistent operations in datastore/storage

test/storage/e2e_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library gcloud.storage;
 
 import 'dart:async';
 
 import 'package:gcloud/storage.dart';
 import 'package:googleapis/common/common.dart' as common;
@@ skipping 242 matching lines @@
     var testBucket = generateBucketName();
 
     // Share the same storage connection for all tests.
     var storage = new Storage(httpClient, project);
 
     // Create a shared bucket for all object tests.
     return storage.createBucket(testBucket).then((_) {
       return runE2EUnittest(() {
         runTests(storage, storage.bucket(testBucket));
       }).whenComplete(() {
-        storage.deleteBucket(testBucket);
+        // Deleting a bucket relies on eventually consistent behaviour, hence
+        // the delay in attempt to prevent test flakiness.
+        return new Future.delayed(STORAGE_LIST_DELAY, () {
+          return storage.deleteBucket(testBucket);
+        });
       });
     });
   });
 }